This question is about amines - AQA - A-Level Chemistry - Question 1 - 2019 - Paper 2
Question 1
This question is about amines.
1 1 1. Give an equation for the preparation of 1,6-diaminohexane by the reaction of 1,6-dibromohexane with an excess of ammonia.
1 1... show full transcript
Worked Solution & Example Answer:This question is about amines - AQA - A-Level Chemistry - Question 1 - 2019 - Paper 2
Step 1
Give an equation for the preparation of 1,6-diaminohexane by the reaction of 1,6-dibromohexane with an excess of ammonia.
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Answer
The reaction can be represented by the following equation:
Complete the mechanism for the reaction of ammonia with 6-bromohexylamine to form 1,6-diaminohexane.
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The mechanism involves the nucleophilic attack of ammonia on the carbon atom bonded to the bromine. The base (NH₃) attacks the electrophilic carbon center, resulting in the displacement of bromide ion and forming 1,6-diaminohexane.
The structure of a possible cyclic secondary amine includes a six-membered ring with a nitrogen atom in the structure, such as pyrrolidine.
Step 3
Stage 1 reagent and condition
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Stage 1 reagent: KCN or NaCN
Stage 1 condition: Aqueous alcohol or reflux
Step 4
Stage 2 reagent and condition
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Stage 2 reagent: H₂ with Ni or Pt or Pd
Stage 2 condition: Reflux under hydrogen atmosphere
Step 5
Explain why 3-aminopentane is a stronger base than ammonia.
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3-aminopentane possesses additional alkyl groups which donate electron density to the nitrogen atom, enhancing its nucleophilicity. This increased electron density makes the nitrogen more willing to accept protons compared to ammonia.
Step 6
Justify the statement that there are no chiral centres in 3-aminopentane.
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3-aminopentane does not have any chiral centers as the nitrogen atom is bonded to two hydrogen atoms and one alkyl group. Therefore, it does not meet the criteria for chirality, which requires four different substituents on a carbon atom.
